June 1995
LM1291
Video PLL System for Continuous-Sync Monitors
General Description
Features
Y
Wide continuous autosync rangeÐ22 kHz to 125 kHz
(1:5.7) with no component switching or external adjust-
ments
The LM1291 is an integrated horizontal time base solution
specifically designed to operate in continuous-sync video
monitors. It automatically synchronizes to any H frequency
from 22 kHz to 125 kHz and provides the drive pulse to the
high power deflection circuit.
Y
No manufacturing trims requiredÐinternal VCO capaci-
tor trimmed on chip
Y
Y
Y
Y
No costly high-precision components needed
Low phase jitter (1.3 ns at 100 kHz)
DC controlled H phase and duty cycle
Video mute pulse for blanking during H frequency
transitions
Available sync processing includes a vertical sync separator
and a composite video sync stripper. An internal sync selec-
tion scheme gives highest priority to separate H and V sync,
then composite sync, and finally sync on video; no external
switching between sync sources is necessary. The LM1291
provides polarity-normalized H/HV and V sync outputs,
along with logic flags which show the respective input polar-
ities.
Y
Y
Y
Y
Input sync prioritization
Clamp pulse position and width control
Continuous clamp pulse output, even with no sync input
Resistor-programmable minimum and maximum VCO
frequency
The design uses an on-chip FVC (Frequency-to-Voltage
Converter) to set the center frequency of the VCO (Voltage-
Controlled Oscillator). This technique allows autosync oper-
ation over the entire frequency range using just one opti-
mized set of external components.
Y
X-ray input disables H drive and mutes video until V
powered down
CC
Y
Y
k
9.5V
H drive disabled for V
CC
The system includes a second phase detector which com-
pensates for storage time variation in the horizontal output
transistor; the picture’s horizontal position is thus indepen-
dent of temperature and component variance.
Horizontal output transistor protected against accidental
turn-on during flyback
Y
Capacitor-programmable frequency ramping, df /dt,
VCO
H output transistor during scanning mode
protects
changes
The LM1291 provides DC control pins for H Drive duty cycle
and flyback phase.
Connection Diagram
TL/H/12323–1
FIGURE 1
Order Number LM1291N
See NS Package Number N28B
C
1995 National Semiconductor Corporation
TL/H/12323
RRD-B30M115/Printed in U. S. A.